For the first time have got stuck with the following puzzle from NZ Herald 20/8/05 rated hard. The hint from Daily Sudoku was 6 in col 9, row 8. I just cannot work out why. Would really appreciate some enlightenment from someone smarter than me!

5 not in r1c3, it is in r2c1 or r3c1 (Column on 3x3 Block interaction)
5 not in r2c3, it is in r2c1 or r3c1 (Column on 3x3 Block interaction)
5 not in r3c3, it is in r2c1 or r3c1 (Column on 3x3 Block interaction)
9 not in r8c8, it is in r8c9 or r9c9 (Column on 3x3 Block interaction)
9 not in r9c8, it is in r8c9 or r9c9 (Column on 3x3 Block interaction)
1 not in r9c3, Hidden Pair 5 7 in r8c3 and r9c3 (in Column)
2 not in r8c3, Hidden Pair 5 7 in r8c3 and r9c3 (in Column)
2 not in r9c3, Hidden Pair 5 7 in r8c3 and r9c3 (in Column)
2 not in r7c7, it is in r7c1 or r7c3 of the 3x3 (3x3 Block on Row/Column interaction)
1 not in r9c7, Hidden Pair 2 7 in r8c7 and r9c7 (in Column)
3 not in r8c7, Hidden Pair 2 7 in r8c7 and r9c7 (in Column)
3 not in r9c7, Hidden Pair 2 7 in r8c7 and r9c7 (in Column)
6 not in r8c7, Hidden Pair 2 7 in r8c7 and r9c7 (in Column)
6 in r8c9 - Unique Horizontal

Hi
Thanks for that!!
The bit I missed was staring me in the face - ie the 2's in row 7 had to be in either col 1 or 3. (I also had it as a possibility in col 7.) Eliminated the incorrect 2 and it all fell into place!
Cheers